Can winemakers defeat the climate models that are predicting their demise?

Extreme weather events like the California wildfires, and climate change, will increasingly threaten vineyards.
Extreme weather events like the California wildfires, and climate change, will increasingly threaten vineyards.
Image: Reuters/Jim Urquhart
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Climate change will severely impact premium wine production zones globally. Yet climate and crop models often lack the resolution needed to reliably project grape suitability loss. Wine producers may still be able to adapt their practices so that the wine of tomorrow remains the wine of today.

 There have been a host of academic articles recently pointing to the impacts of climate change on wine production. Some authors have offered up a doomsday scenario for the premium wine production areas of the world, estimating losses in grape suitability between 25% and 70%.

Others have highlighted potential opportunities, demonstrating that warmer temperatures have allowed for quality wines to be produced without the prerequisite drought conditions commonly associated with fine vintages. Areas from upstate New York to southern England — hardly considered wine Meccas — have been slated as potential premium growing regions in to the future.

While the regional winners and losers may take some time to pan out, that change is underway is undeniable. Compared to 1980, for example, average wine harvests today come ten days earlier. In Bordeaux, France, this has been accompanied by earlier budding, flowering, and ripening — and shorter durations between these events — changing the duration of growing and ripening seasons.

Most studies using climate and crop suitability modeling show that grape growing regions are expected to shift into cooler zones, to the north in the northern hemisphere and further south in the southern hemisphere. It is entirely possible, for example, that Bordeaux’s 2050 climate, currently home to an abundance of Cabernet Sauvignon and Merlot grapes, may be found in the modern day Loire region of France. White grapes in Loire, in turn — not too unlike coffee and chocolate — may slowly run out of real estate altogether in France.

But before you go buying land in the Adirondacks and the outskirts of London, it’s worth taking a moment to discuss the science behind climate and crop modeling, and to highlight the ways that wine producers are already adapting to changing climates. Wine producers, like grapevines, after all, are tougher than they look.

Climate change modeling

Climate change is happening. The World Meteorological Organization has confirmed that 2016 was the hottest year on record, and each passing month seems to confirm the trend. The northern hemisphere, according to the Intergovernmental Panel on Climate Change (IPCC), has seen the warmest 30-year period (1983–2012) in nearly 1500 years. Average global temperatures have increased by 0.85 degrees Celsius (°C) in the last century, and given the current rate of CO2 emissions, we’re on pace to see an exponential rise in average temperatures of 3–4°C, well beyond the 1.5–2°C threshold scientists consider ‘safe’. As a result, we’ve already seen an increase in extreme events associated with climate change, unprecedented sea level rise, and increased drought and flood events. Given these trends, it is very likely that so-called “100 year weather events” will occur a 10–20 year intervals by the end of the century.

To determine what our climate may look like in to the future, scientists use a variety of modeling tools. Most studies of future wine grape (Vitis vinifera) suitability rely on several such modeling inputs. First, global Green House Gas (GHG) emissions scenarios are identified, differing according to projected demographic and economic trends as well as potential technological developments in the world. These scenarios are either more or less optimistic about our collective efforts to transition to a greener economy and can help modelers determine how much energy will be available in the climate system.

Second, these energy assumptions are used to produce atmospheric and oceanic ‘general circulation models’ (GCMs) that account for complex feedback loops between temperature, precipitation, solar radiation, and a host of other variables that contribute to the earth’s climate system. GCMs provide scientists with projected conditions within a grid on the earth’s surface (usually a few hundred square kilometers) that can be visualized using geographic information systems software. These are the colorful maps we often see in climate reports.

Finally, GCM data on temperature and precipitation can then be fed into crop models that take in to account the required growing conditions of a particular plant at different phases of its development. All told, to produce the suitability results we see in most studies, at least three separate phases of analysis are required, each drawing on a host of variables.

Vitis Vinifera

 — no friend to climate models

Climate and crop modeling have made considerable advances in the past 20 years. Models have benefitted and improved their ‘skill’ through model inter comparison, and so-called ‘ground truthing’ using observed and historical trends. Despite immense progress, both climate and crop models are still wrought with assumptions and are generally considered most informative at a continental scale. In informing decision making, these tools should be considered carefully together with other evidence. This is especially true in the agricultural sector. Consider the limitations of these models and the unique climatic characteristics of premium grape growing regions:

First off, climate models work in averages and outlier events matter in agriculture. For example, an increase in mean summertime temperatures across Bordeaux of 4°C may indeed push vines to their physiological limits (thus creating a very fine i.e., high quality, wine), while a single extreme heat event during flowering will destroy that year’s crop entirely. These events are lost in averages. Daily and hourly changes in weather can affect grape production and vintage quality, and frost, hail, and heavy rainfall events — more difficult to model than temperature increases — have equally harmful effects on grape production.

Second, GCMs produce data at a very low resolution — so low, in fact, that some scientists have suggested that it may take upwards of 50 years for climate models (especially precipitation) to be able to meaningfully contribute to agricultural impact modeling. This is because while it’s practical for some uses and sectors to consider impacts as they occur at a scale of hundreds of kilometers, this is not true for viticulture. As any grape grower will tell you, micro-climates are of severe consequence to wine quality, and the difference between a good vintage and a bad one is a matter of feet, not kilometers. Ultimately, both seasonal and spatial variations in climate are critical and are often not accurately depicted by these global models.

Finally, Vitis vinifera is a fickle creature. Premium varieties are grown in a very narrow latitudinal band, approximately 35–50 degrees north and south of the equator. Each year they require 165 safe growing days between 12° C and 22° C. For truly premium production, grapes often need dry, warm periods just before harvesting and cool — but not too cold since grapes can’t usually withstand temperatures below -10°C — winter for the plant to rest and to fend off disease (grape vines are very vulnerable to fungal pathogens during rainy, winter months).

Fine vintages rely on a delicate balance between acids and sugars (the higher the sugar content, the greater the alcohol content) that can be disrupted by rainfall during ripening, increasing the physical size of the berry. Then there is the important question of sunshine. Grapes that receive a lot of direct sunlight tend to mature faster and give a full-bodied flavor to wine (hence the preference for gently sloping, southern-facing vineyards). Scientists can quite accurately project solar radiation, but cloud cover is a more challenging variable to account for.

There is, then, a very precise series of conditions that must be met for fine wine to emerge. While there is general consensus between models that grapes will be pushed to their physiological temperature limits in premium growing zones, these micro-climatic considerations important to wine production are not easily captured.

Grapes are tough, farmers are tougher

Unpredictability has been a part of wine growing for as long as the profession has existed. There is no doubt that many vintners will successfully adapt to the changing circumstances presented by climate change. This sentiment is not intended to lull producers in to false sense of security, as grape suitability in existing premium zones will get better before it ultimately get much worse. There are, after all, very real limits — or thresholds — to adaptation that are determined by basic plant physiology. There remain many variables, however, squarely within the control of modern day farmers.

To be sure, climate and weather are the main factor in determining wine quality. One study from 2004 suggests that climate and soil type account for 75% of wine’s quality, with climate considerations contributing over 50% alone. But climate is only one part of the equation for wine producers. Wine connoisseurs speak often of ‘terroir’, roughly translating to the mix of climate, terrain (land and soil), and culture that determine where and what type of wine is produced. The term, often evoking images of a sun-soaked, rolling landscapes and rocky soil spilling through a vintner’s hands, actually speaks scientifically to a grape’s basic physiology and phenology (the seasonal stages of a plant’s growth).

Dark, dry, rocky soils, for example, while not suitable for some crops, allow grape root systems to grow deep, improving the quality of wines and allowing vines to survive important quality-producing drought events. Soil composition is also responsible for giving wines their unique regional flavors. Soil should drain well, but retain some moisture to keep the soil medium cool.

Proximity to a body water is also an important factor for irrigation, humidity, and temperature moderation. Shifting production zones will have to take into account these important considerations along with the broader climate drivers. New varieties and rootstocks adapted not only to heat but different soil regimes, for example, will be necessary.

Several adaptation strategies are already being adopted by viticulturists to combat climate change, ranging from row management to wind machines and heaters and the use of falcons and drones to deal with new pests. Adjustments to pruning, trellising, and harvest timing — including selective, staggered harvesting — are among just a few obvious examples. During especially warm seasons, for example, vine canopies can be trimmed less (or later than normal), increasing shade, and reducing solar radiation, ultimately slowing grape maturity and reducing the risk of ‘sunburn’.

Diversifying the orientation of new vine rows (east-west, north-south and in between), planting on north-facing slopes and in low-lying zones represent alternative adaptation measures that reduce heat and sun exposure. Similarly, the addition of irrigation infrastructure (farmers in Australia have organized a recycled water scheme) and improved drainage in fields can help to adjust to rains that tend to arrive more intermittently and in heavy bursts. Increased use of perennial and annual covercropping can help to mitigate the impacts of intense rainfall, as well as reducing fungal growth, and combating competitive weeds (an alternative to chemical weeding). Finally, planting certain flowers between rows can also bring in predatory species to limit new pests and diseases that results from climate change.

These management actions have important tradeoffs, however. Late and reduced canopy trimming for heat protection, for example, reduces airflow and can increase the risk of fungal infection when combined with increased rainfall. Similarly, planting in low lying, cooler terrain increases the risk of frost vulnerability. Covercrops, meanwhile, can reduce daytime heat absorption in soils, reducing nighttime temperatures and increasing the risk of frost events.

Given the limitations of management-level adaptations, most producers will need to begin establishing heat-tolerant varieties of grapes. Late ripening varities that require more heat for bud-break, in particular, may be chosen. Merlot or Pinot Noir are especially vulnerable to heat stress as they ripens earliest in the season. These varieites could be replaced with the lesser Petit Verdot or Marselan hybrid varieties, for example.

Other hybrid varieties of grapes (and grape blends on the production side) will inevitably emerge. Grape varieties that historically proved difficult to bring to maturity in a shorter growing season — like Malbec, Tibouren, Cinsault, and Rolle — may also be adopted anew. The process of varietal change will take considerable time as grapes need up to five years from planting to produce fruit, and generally only get better with age (the older the vine, the better the wine). In other words, for new grapes to rescue premium growing regions, the process needs to start today.

In adapting to climate change, wine producers will also face socio-political barriers. The types of grape that are formally associated with a production zone in France, for example, is determined by formal designations of origin (appellation d’origine contrôlée), or AOC, as determined by the French government, National Institute for Quality and Origin.

Currently, the AOC allows for six red grapes to contribute to the prestigious Bordeaux label, although the Bordeaux wine board has petitioned to add four new varieties. Additionally, French law requires that wines under a given appellation be grown, processed, and bottled in that same zone. This means that should there be a shift in production zones that new varieties cannot prevent, that production infrastructure will have to follow.

There will inevitably remain a place for tradition, but a certain amount of flexibility must be afforded to producers (in Australia, up to 15% of grapes in a given appelation can come from outside the geographic zone, for example). Unless the region’s institutions are as flexible and adaptive as farmers, it’s likely that the rate of change will outpace the region’s ability to adapt.

Viticulturists can reduce the heavy lifting of adaptation if they work to prevent GHG emissions from their own farms in the first instance. The global agricultural sector more broadly is responsible for approximately 25% of total emissions when land use changes associated with deforestation are included. That’s more than the transportation and manufacturing sectors combined, and second only to the global energy sector.

Wine producers, specifically, are responsible for considerable nitrous oxide (N2O) emissions (a very powerful GHG) through nitrogen fertilizer application on vineyards. The collective actions of small organic and climate-smart winemakers, then, can have a major impact on whether this climate future will become reality. Vintners of all sizes have a vested interest in limiting the affects of climate change. Their choices — along with every other major GHG producing sector — will determine whether their vineyards remain viable.

It has been said,“it takes bad vintages to judge a good winegrower”. This may become an increasingly relevant statement in much of the world’s premier wine producing regions. Wine has been the fermented drink of choice for over 8,000 years. With a cautious use of climate models and clear adaptation strategies innovative producers will help to ensure that the wine of tomorrow may still be recognizable.